I knew this from day one he said open world. It was funny to watch dumb ass fanboys getting excited thinking it will be open world like Skyrim or GTA 5. That wouldn't work in a MGS game. What Snake running over civilians and going on mindless rampages lol

I belive it'll be just like Portable Ops where you can pick your missions on a big scale map. The open worldness of it will come from your freedom of choosing in what order you can do the missions, or in what way you'll achive the goals along with in what ways you'll reach your destination (stealth at night/morning, going rampage, using vehicles etc.). I don't think Kojima is taking the GTA route with it, that style of gameplay wouldn't suit an MGS game very well- this "controlled" open-world mechanic would be a better choice as MGS games still depend on story progression rather than map domination.

I guess it'll still be a corridor game, with corridors being considerably larger than how they were in previous games.

It is true that it will consist of separate areas, accessible by helicopter, but those areas itself are going to be large and open. Look at the gameplay for the Afghanistan level for example, I wouldn't call that a corridor. This is something that hasn't been done before in the series.